The small cell technology uses low-power wireless access nodes to extend the coverage range of a macro cell, distributes growing data flow of the macro cell, and increases the utility efficiency of radio spectrum resources. The LTE-Advanced system uses this technology to increase network capacity.
Typically, the Small Cell has a small size, and its coverage range is between 10 meters to 2 kilometers. The Small Cell deployment scenario in the LTE network is composed of two levels: macro cell and small cell. The macro cell and the small cell can be deployed at the same frequency point, that is, co-channel deployment; or they can be deployed at different frequency points, that is, non-co-channel deployment; alternatively, the macro cell may not be deployed, and only the small cell is deployed. The small cell can be deployed in indoor environments and outdoor environments. It may be deployed sparsely or densely.
The Small Cell is an interference-limited system, there are complex interference relationships between the macro cell and micro cell, as well as between the micro cell and the micro cell. Each cell dynamically schedules to serve terminals within the cell. In addition, as the UE moves, there are UEs continuously moving in and moving out of the small cell, the load and interference of the Small Cell system will show a significant fluctuation. Therefore, it must adopt a certain interference coordination method, such as small cell adaptive switching mechanism and adaptive power adjustment mechanism, to suppress and coordinate the interference in the Small Cell.
The basic idea of the small cell adaptive switching mechanism is adaptively opening or closing some small cells with very low load to reduce inter-cell interference. An opened cell is called an activated cell, and a closed cell is called a dormant cell. The activated cell normally transmits data channels and common channels; the dormant cell closes data channels and some of common channels. However, both the activated cell and the dormant cell can transmit the cell discovery signal (DS) that is used for the cell discovery and selection, activation/deactivation judgment, and so on. The discovery signal is still under discussion, currently there are several viewpoints: 1) following the traditional PSS/SSS/CRS (Primary/Secondary Synchronization Signal, Cell-specific reference signals) signal; 2) using the modified PSS/SSS/CRS signal; and 3) using a new DS.
The UE detects the DS of the activated cell and the dormant cell to discover and select a cell. For a dormant cell, if there is a UE detecting the discovery signal of a cell, it indicates that there are UEs existing under the coverage of the cell, and it may consider to activate the cell in order to serve these UEs. For an activated cell, if the UE detects the DS signal of a cell, if the DS signal of the cell is stronger than the DS signal of the current serving cell, it may consider switching to the cell; or although the DS signal of the cell is equivalent to or relatively weaker than the DS signal of the current serving cell, but for the load balancing consideration, if necessary, it may also consider switching to the cell. Therefore, the DS measurement is very important for operations such as discovery, selection, activation and deactivation of a small cell system. The DS measurement method can be a presence/absence detection, namely 0/1 detection, and it takes how many times it is detected within a certain time period as a measurement value; it can be a quantitative detection, that is, the RSRP (Reference Signal Receiving Power) detection/RSRQ (Reference Signal Receiving Quality) detection/SINR (Signal to Interference plus Noise Ratio) detection that takes the DS signal intensity or signal quality as the measurement quantity.
There are different measurement needs for performing the DS presence/absence detection and the DS intensity detection, the number of samples required in the presence/absence detection is small, while the number of samples required in the intensity detection is large and the filtering time is longer, that is to say, the presence/absence detection and the intensity detection need to use different measurement patterns. In addition, for a scenario in which the Small Cells are deployed at different frequencies, the UE needs to carry out an inter-frequency detection on the DS of the inter-frequency cells. In the Measurement Gap of an inter-frequency detection, the UE needs to switch to a measurement frequency point different from its working frequency point, at this time it needs to stop transmitting data temporarily. From the viewpoint of spectrum efficiency, it should shorten the measurement gap as much as possible. Currently the DS measurement is still under discussion, and different measurement patterns are not provided for these different measurement needs in the related art. Therefore, it is necessary to study a method for configuring measurement patterns of discovery signals.